The present invention relates to a luminaire for a bicycle and more particularly to a bicycle light fitting which does not require any frictional engagement with a wheel tire and use of any storage batteries.
Conventionally, a luminaire or light fitting for bicycles has an unipolar electric generator having a rotary shaft adapted to be frictionally engaged with a side of the wheel tire so that a rotational energy of the rotary shaft by rotation of the wheel is converted to an electric energy to light a bulb of the luminair. This light fitting has long been used as it can be made simple. However, it is troublesome to operate the rotary shaft to be releasably frictionally engaged with the tire. Moreover, the conventional light fitting requires another manpower for driving the rotary shaft with additional load by rotating the bicycle wheel in addition to the power required for simply driving the bicycle, and troublesome maintenance and repairement of brushes in the generator are needed. Further, the frictional engagement of the rotary shaft with the tire results in wearing of the tire and produces an unfavorable noise. In order to avoid such disadvantages as described, an attempt has been made to use dry cells as developments in the life of the dry cells, but the light fitting using dry cells still has a serious porblem of the limited life of the dry cells and troublesome manipulation for changing them with new ones.
Wiegand effect technology exploits magnetic properties of specially processed, small diameter ferromagnetic wire, which is nominally 15-30 mm in length, and diameter of about 0.25 mm. The wire, generally of iron-cobalt-vanadium composition, is cold-worked and tempered according to a process developed by John R. Wiegand. Transducers utilizing this effect require a few simple components to produce sharply defined voltage pulses in responses to changes in the applied magnetic field. In the simplest form, transducers consists of a short length of Wiegand wire, a sensing coil and actuating magnetic fields that generally are derived from relatively small permanent magnets.
Processed Wiegand wire has a permanently work-hardened surface, that is, a shell, and a relatively soft inner core. The shell exhibits high magnetic coercivity and, therefore, requires a strong magnetic field to change its direction of longitudinal magnetization. The core has low coercivity, and its direction of magnetization can be changed easily without affecting the magnetic polarity of the shell. By properly manipulating external magnetic field excursions, the core and the shell can be switched to the same or opposite state of magnetic polarity. The polarity switching occurs abruptly and therefore this provides the so called Wiegand effect.
It is known that the Wiegand wire in combination with a permanent magnet and a detection coil can generate a relatively large electric pulses by utilization of the Wiegand effect. A switching operation mode will be explained with reference to FIGS. 4A, 4B and 4C. The Wiegand wire has a shell 1 and a core 2. In the drawing, reference numeral 3 represents a magnetic field of the Wiegand wire. FIG. 4A shows a state in which the Wiegand wire is magnetized in one direction at the shell and the core by a magnet (not shown) of a strong saturation flux density. FIG. 4B shows a state in which the magnetization in the core 2 only is reversed by a reset magnet of a relatively weak magnetic field, and FIG. 4C shows a state in which the first-mentioned magnet of a strong saturation flux density is again applied to thereby cause the magnetization state of the core to be returned to the initial state of magnetization.
In FIG. 5 which shows output pulses induced to a sensing coil (not shown) disposed adjacent to the Wiegand wire. Negative pulses shown by reference numeral 4 are generated at the state shown in FIG. 4B in which the magnetization polarity in the core is switched. The core 2 and the shell 1 are mutually affected to each other in respect of their magnetic fields to generate a relatively slow change in the magnetic polarity and consequently a relatively slow change in magnitude of the voltage pulse generated by the sensing coil is proportional to the change of magnetic flux by time. Consequently, the slow change in magnetic flux as described above will induce a relatively small electric voltage in the sensing coil. Positive pulses 5 are generated at the state of FIG. 4C. In this state, the core 2 and the shell 1 are magnetically affected to each other to produce a relatively rapid change in magnetic polarity and consequently a large voltage pulse is induced in the sensing coil.